During downhole operations, such as drilling and reaming, drilling fluid is pumped through a drill string to a downhole tool. The fluid flows into the annulus of the wellbore through one or more ports or nozzles in a drill bit or other downhole component. The fluid then flows back up to the surface through the annulus, which is located between the downhole tool and the wellbore wall. In a drilling, milling, underreaming, or other similar operation, the fluid may carry cuttings or swarf back to the surface.
In some downhole operations, the fluid may flow into the wellbore annulus through ports or nozzles installed in reamers or flow splitter tools. The properties of the fluid (e.g., flow rate, viscosity, density) may affect the performance of the downhole tool. For example, the properties of the fluid may affect the drag on the downhole tool, the attenuation of mud pulse telemetry signals transmitted from or received by the downhole tool, the output of turbines and/or motors in the downhole tool, and the like. Flow meters, viscometers, densitometers, and other downhole fluid sensors may be used to measure the properties of the fluid (e.g., flow rate, viscosity, and density, respectively).